1. Field of the Invention
The present invention relates to a tape recorder. More particularly, the present invention relates to a head drum assembly for a tape recorder and a method of assembling the same that urges a rotary drum at a constant pressure and maintains a constant spacing between a rotor and a stator.
2. Description of the Related Art
In general, a tape recorder, such as a video cassette tape recorder or a camcorder, operates to record and reproduce image and sound data on and from a magnetic tape that is wound around a pair of reels and is moved along a certain path. Such a tape recorder includes a head drum assembly for writing or reading a signal on or from the magnetic tape by scanning of a magnetic head rotated at high speed.
FIG. 1 shows one example of a conventional head drum assembly for a tape recorder.
Referring to FIG. 1, the head drum assembly includes a stationary drum 1, a shaft 3 fixed to a center of the stationary drum 1, a rotary drum 7 installed to an upper portion of the stationary drum 1 and rotated by the shaft 3, and a drum cover 13 installed to an upper portion of the rotary drum 7 and fixed to the shaft 3. The rotary drum 7 is rotatably supported on the shaft by two ball bearings 11, and includes a magnetic head 9 for writing the signal on the magnetic tape or reading the signal from the magnetic tape. Rotary transducers 5 are installed to a lower portion of the rotary drum 7 and the upper portion of the stationary drum 1 to transmit or receive the signal to or from the magnetic head 9 in such a way that the transducers are facing one another. A rotor 20, which is a component of a motor, is fixed to the upper portion of the rotary drum 7. A stator 21 is positioned opposite the rotor 20 and connected to a lower portion of the drum cover 13, so that the rotary drum 7 is rotated by operation of the motor.
In order to stably rotate the rotary drum 7, the rotary drum 7 is installed such that a constant preload is applied to the ball bearings 11 supporting the rotary drum 7. According to a conventional method of applying the preload to the ball bearing 11, a protrusion 15 is formed on a lower surface of the drum cover 13 to press an inner race of the ball bearing 11. After the protrusion 15 is inserted into the shaft 3, a certain weight is positioned on the upper portion of the drum cover 13 such that the protrusion 15 applies the preload to the ball bearing 11. Then, the drum cover 13 is fixed to the shaft 3 by means of a fastening element 17, such as a screw. As such, the drum cover 13 presses the inner race of the ball bearing 11 at a constant pressure so that the ball bearing 11 is constantly preloaded.
In this situation, supplying power to the stator 21 of the motor rotates the rotor 20, which causes the rotary drum 7 to rotate at a fast speed. The magnetic head 9 fixed to the rotary drum 7 transmits and receives the signal to and from a controller of the tape recorder through a rotary transducer 5 to write the signal on the magnetic tape or read the signal from the magnetic tape.
Rotating the rotary drum 7 at a high speed generates an increasing amount of force on the rotary drum 7. A preload acting on the ball bearing 11 at the rotation of the rotary drum is different from the preload predetermined at a stationary state of the rotary drum. Specifically, the preload set to stably rotate the rotary drum 7 is varied, thereby causing the rotary drum 7 to be unstable.
In addition, since the preload is constantly applied to the ball bearing 11 by pressing the inner race of the ball bearing 11 with the protrusion 15 of the drum cover 13, the spacing between the stator 21 and the rotor 20 that form the motor is varied depending upon machining dimensions of the drum cover 13 and assembling tolerances of the rotary drum 7. Thus, a problem exists because the spacing between the stator and the rotor is not constant in every head drum assembly.
Also, a control circuit board 23 is fixed to the drum cover 13, as well as being fixed to the stator of the motor 21. The method of fixing the drum cover 13 to the shaft 3 using the screw 17 may cause signals, for example, FG signals, PG signals, etc., for controlling the motor (that is, FG. PG, etc) to be unbalanced due to the circuit board being distorted of the circuit board occurring during fastening of the screw 17.